Desoxycholic acid as a separating agent



United States Patent DESOXYCHOLIC ACID AS A SEPARATING AGENT Ralph B.Thompson, Hinsdale, Ill., assignor to Universal Oil Products Company,Des Plaines, 111., a corporation of Delaware No Drawing. ApplicationOctober 4, 1956 Serial No. 613,806

10 Claims. (Cl. 260-676) carbons from mixtures of the same withrelatively more .-,branched chain and cyclic hydrocarbons by a methodwhich comprises contacting the hydrocarbon mixture with discreteparticles of desoxycholic acid and thereafter withdrawing as a raflinatestream the components of the hydrocarbon mixture having relativelybranched chain and .cyclic structure.

One embodiment of the present invention relates to -a process forseparating an aliphatic hydrocarbon of relatively lesser branched chainstructure than other components of a mixture of hydrocarbons from saidother ,hydrocarbon components which comprises contacting said mixturewith desoxycholic acid and thereafter separating a fraction enrichedwith respect to at least one of said other hydrocarbon components.

6 A more specific embodiment of this invention concerns a method forseparating a normal parafiin containing from to about 20 carbon atomsper molecule from branched chain paraflinic and cyclic hydrocarbonswhich comprises introducing a hydrocarbon mixture comprising said normalparaffin and a hydrocarbon component selected from said branched chainand cyclic hydrocarbons into contact with desoxycholic acid at atemperature of from about 0 to about 120 C. and at sufiicient pressureto maintain the hydrocarbon mixture in substantially liquid phase andthereafter recovering a raflinate comprising a hydrocarbon selected frombranched chain paraflinic and said cyclic hydrocarbons from adesoxycholic acid complex of said normal parafiin and recovering thenormal paraffin from said complex by contacting the complex withn-pentane at the aforementioned temperature and pressure conditions.

" The present process for separating hydrocarbon mixtures is dependentupon the selective action of a specific organic compound, that is,desoxycholic acid, in selectively combining with aliphatic hydrocarbonsof relalieved to be an adduct or complex between the acid and thehydrocarbon, although the present process is not intended to benecessarily limited in its scope to such explanation of the activity ofthe desoxycholic acid as a separating agent. In any event the net effectof contacting the desoxycholic acid with a hydrocarbon mixtureloontaining relatively straight chain aliphatic components as well asbranched chain and/or cyclic components'is the selective retention ofthe relatively straight chain hydrocarbons and the rejection into araflinate phase of the branched chain and/or cyclic hydrocarbonscontained in the mixture.

Suitable hydrocarbon feed stock mixtures utilizable in the. presentseparation process include any hydrocarbon said v tively straight chainconfiguration to form what is be- I mixture containing normal orrelatively straight chain aliphatic components of parafiinic, olefinicor diolefinic structure in admixture with one or more members of thegroup comprising the aliphatic hydrocarbons of more highly branchedchain structure than the component to be separated, naphthenichydrocarbons or aromatic hydrocarbons of monoor bicyclic ring structure.A particularly useful application of the process is in the treatment ofgasoline boiling range fractions for the purpose of increasing theoctane number of the fraction by removing the relatively non-branchedchain aliphatic hydrocarbons which have the lowest octane rating of thevarious classes of hydrocarbons and which reduce the octane rating ofgasoline boiling range fractions in which these hydrocarbons occur.Thus, by subjecting a mixture of hydrocarbons boiling in the gasolinerange to treatment With the present separating agent, the effluent fromthe process contains a relatively greater proportion of the more highlyoctane rated isoparaflinic and cyclic hydrocarbons than the feed stockmixture because of the selective removal of the normal or relativelystraight chain aliphatic components from the mixture. The bydrocarbonsthus removed from the gasoline fraction by the present separating agentmay be separately recovered and subjected to a suitable conversionprocess, such as an isomerization or a reforming process to convert therelatively straight chain hydrocarbons thus recovered into branchedchain or cyclic isomers of higher octane number. The process, ingeneral, is applicable to hydro- .carbon fractions containing componentshaving at least ing temperatures) is utilized in the process, it ispreferably diluted with a C C and/ or C branched chain or cyclichydrocarbon diluent in order to reduce the viscosity of the chargestock.

A convenient method of operating a contacting type of separationprocess, suitable for use with the present reagent, comprises mixing thedesoxycholic acid separating agent with the hydrocarbon mixture inliquid phase and thereafter filtering the resulting mixture to recoverthe separating agent containing adsorbed or occluded thereon the normalor straight chain aliphatic hydrocarbon components of the mixture. Sincethe present desoxycholic acid separating agent is substantiallyinsoluble in the hydrocarbon feed stock mixture, another means ofoperating such a separation process comprises passing the hydrocarbonfeed stock through a column packed with discrete particles of thedesoxycholic acid until the latter has adsorbed sufiicient normal orstraight chain aliphatic hydrocarbons to substantially saturate thecapacity of the separating agent to adsorb additional hydrocarbon. Inthis type of separation the desoxycholic acid separating agent may becomposited with or deposited on a suitable solid supporting material,such. as charcoal, sand, quartz chips, brick, Beryl saddles or othersolid, generally porous material, insoluble in the hydrocarbon stream.The latter adsorption type procedure may be effected under liquid-solidphase conditions or gas-solid phase conditions, depending upon thetemperature of the feed stock and the ambient pressure. In eithermethod, the temperature of operation must be such that the separatingagent is maintained in the apparatus in substantially solid phase, thatis, at a temperature below the melting point of the normally soliddesoxycholic acid. At atmospheric pressures, the contacting temperatureis preferably maintained within the range of from about 20 to about C.although higher or lower temperatures are also feasible. For

most hydrocarbon mixtures, however, temperatures in the above-indicatedrange and pressures in the region of atmospheric pressure are suitablefor effecting the separation. In a gas-solid phase type'of separation,the feed mixture in gaseous phase is introduced into the apparatuscontaining the desoxycholic acid as a 'stationary, packed bed (theso-called fixed bed technique) or the velocity of the gas phase may besuflicient to continuously suspend the desoxycholic acid in thehydrocarbon gaseous phase (the so-called fluidized 'bed technique). Inmany moving bed procedures, either the fluidized or compact moving bedmethods, countercurrent flow arrangements may be effected by chargingthe fresh feed stock into one end of the apparatus and charging fresh orregenerated absorbent into the other end. The spent adsorbent containingthe relatively straight chain components of the mixture adsorbed on thedesoxycholic acid is removed from the end of the apparatus into whichthe fresh feed is introduced. Still another effective methodofseparation comprises mixing the hydrocarbon feed stock with an aqueousslurry of desoxycholic acid in finely divided condition and thereafterallowing the resulting phase separation to take place, the normal orrelatively straight chain hydrocarbon components of the feed stockentering into combination with the desoxycholic acid to form awater-insoluble, solid phase component of the slurry, while therelatively branched chain or cyclic hydrocarbon components of the feedstock form a separate, liquid phase which may be decantedor'centrifuged' from the slurry. Instead of utilizing water as thesuspending medium for the slurry, a hydrocarbon having -a boiling pointabove or below the feed stock mixture may be substituted for the waterto provide the fluid phase, 'thenon-adsorbed, branched chain or cyclichydrocarbon components of the feed stock mixing with an excess-of theliquid hydrocarbon to form an efliu'en't ratfinate phase which may bedistilled or otherwise treated to separate the added hydrocarbonutilized as suspending medium from the non-adsorbed components of thefeed stock mixture. The preferred hydrocarbons for this purpose are thecyclic and branched chain hydrocarbons of lower molecular weight(therefore, of lower boiling point) than the components of the feedstock mixture. Typical hydrocarbons of the latter type includeisobutane, isopentane, 2,3-dimethylbutane, cyclohexane and its methylorethyl-substituted homologs, or other relatively low molecular Weighthydrocarbons of the class not adsorbed by the present separating agent.

The desoxycholic acid-hydrocarbon adduct or complex formed by adsorptionof the normal or relatively straight chain hydrocarbon component of thefeed stock onithe desoxycholic acid during the separation process may beindividually treated following the separation process in order torecover the adsorbed hydrocarbon, if de'sired.- .For this purpose, theadduct or complex may be heated 'abovethe boiling point of the adsorbedhydrocarb'on to remove the adsorbed hydrocarbon by dis tillat'ion fromthe generally higher boiling desoxycholic acid,"such vaporizationpreferably being effected under reduced pressure in order to increasethe quantity and rateo'f recovery of the adsorbed hydrocarbon. Anothersuitable-method for recovering the adsorbed hydrocarbon compriseswashing the adduct or complex with an excess of a liquid or gaseoushydrocarbon containing or comprising relatively straight chainhydrocarbons which are preferably adsorbed by the desoxycholic acidseparating agent. and'thereafter distilling the resulting hydrocarboneffluent to recover the wash hydrocarbon separate from thenfdesorbedhydrocarbon. In the latter method of rec'overy it is generally preferredto utilize a hydrocarbon washing. agent which boils above or below theboiling point of the adsorbed hydrocarbon (for example, npentane,n-hexane or other relatively straight chain hydrocarbon) in order tofacilitate separation ofthe desorb'ed hydrocarbon from the excessdesorbing hydrocarbon in the wash efiiuent. This recovery operation ispreferably effected under countercurrent flow conditions in order tosubstantially complete the recovery of the adsorbed hydrocarbon from theadsorbent. The spent desoxycholic acid having adsorbed thereon the washhydrocarbon may generally be readily regenerated by heating, steaming orby other methods for restoring the adsorptiveness of the desoxycholicacid for the relatively straight chain aliphatic hydrocarbons of thefeed stock in a succeeding run.

The ratio of desoxycholic acid adsorbent to hydrocarbon feed stockmixture supplied to the separation zone is preferably sufficient toprovide at least 0.1 mol of desoxycholic acid per mol of the hydrocarboncomponent in the feed stock mixture to be separated; that is, a molarratio of desoxycholic acid to the normal or relatively straight chainhydrocarbon component of the feed stock of at least 0.1 to l andpreferably from about 0.5 to 1 to about 3 to 1 'mols per mol.

l The present adsorptive-type separation process may be effected in abatch-type procedure or on a continuous basis, provided that sufiicientseparating agent is maintained in the contacting zone to form a complexbetweenthe desoxycholic acid and substantially all of the normal orrelatively straight chain components of the feed stock mixture suppliedto the separation zone, if substantially complete recovery of thesehydrocarbons from a given-feed stock is desired. Thus, in a typicalbatchtype separation process the desoxycholic acid and the feed stockmixture are charged into a suitably stirred or otherwise agitated vesseland the resulting phases mixed for a period of from /2 to about 2 hoursand thereafter the resulting adduct or complex is recovered from theresulting slurry by centrifuging, filtration or by other means ofseparation well known to the art. In a typical continuous type ofoperation the feed stock mixture and desoxycholic acid are continuouslycharged into an elongated vertical vessel, the separating agent beingpreferably introduced into one end of the vessel, the raffinate efiiuentor stream of unadsorbed components of the feed stock mixture (branchedchain and/or cyclic hydrocarbons) being withdrawn from the same end ofthe vessel that receives the separating agent, while the complex oradduct is withdrawn from the same end of the vessel that receives thefeed stock mixture. The adduct may thereafter be transferred to anothervertical, elongated vessel (preferably into the top thereof) whilea-desorbin'g agent of the aforementioned type is charged into theopposite end of the vessel in order to effect countercurrent desorption,the liquid eflluent being thereafter fractionally distilled or otherwisetreated to elfect separation of the relatively straight chainhydrocarbon recovered from the feed stock from the desorbing or washhydrocarbon.

The present invention is further illustrated with respe'ct to several ofits embodiments in the following examples which, however, are presentedmerely for illustrative purposes and not by way of limiting theinvention.

EXAMPLE I A mixture of 50.1 parts by weight of n-heptane and 49.9 partsby weight of iso-octane was charged into a stirred autoclave, togetherwith 45% by weight of the combined mixture of desoxycholic acid. Theresulting mixture was thereafter stirred at 70 C. for /2 hour, fol lowedby filtering the resulting slurry. The filtrate, con sisting ofunadsorbed hydrocarbon components of the feed stock, was subjected toinfra-red analysis to determine-the proportion of normal heptane andiso-octane components therein. The analysis'indicated that 65% by weightof the filtrate consisted of iso-octane and 35% by weight consisted ofn-heptane.

The filter cake recovered from the above filtering operation was stirredwith 20% of its weight of n-pentane at 70 C. for /2 hour to form'aslurry which was thereafter filtered and the filtrate recovered andanalyzed.

The filtrate consists exclusively of n-pentane and n-hep- EXAMPLE II Aseparation of n-heptane from iso-octane was efiected in the followingrun on a continuous basis and under countercurrent flow conditions bycharging the desoxy- 'cholic acid continuously into the top of avertical column packed with desoxycholic acid, as feed stock mixture iscontinuously charged into the mid-portion of the column.

A solid adduct or complex is continuously withdrawn from the bottom ofthe column, the rate of charging the feed stock mixture being adjustedto provide a n-heptane to desoxycholic acid molecular ratio of 0.5 to 1by ad justing the flow rates of the adsorbent and feed stock mixturestreams into the column. By themethod indicated, utilizing a verticalcolumn 40 inches in height, a "countercurrent fiow arrangement isestablished and the hydrocarbon stream withdrawn from the top -of thecolumn is substantially enriched with iso-octane. A solid desoxycholicacid-n-heptane complex was withdrawn from the bottom of the column as acompressed cake substantially free of liquid phase hydrocarbons.Displace' ment of the adsorbed hydrocarbon from the complex removed fromthe bottom of the column with n-pentane, was effected by utilizingsuflicient n-pentane to form a thin slurry with the complex at 70 C. andthereafter filtering the resulting n-pentane complex from the resultingmixture of excess n-pentane and the displaced nheptane. The n-heptane isrecovered from the mixture by distillation and on the basis of infra-redanalysis of the still residue the n-heptane component is enriched to aproduct containing about 92% by weight of n-heptane by the indicatedcountercurrent contacting method. The iso-octane overhead from the abovecontinuous countercurrent column is enriched with iso-octane to aproduct containing about 95% iso-octane.

EXAMPLE HI In the following run a chromotographic adsorption typeseparation procedure was utilized to determine the effectiveness ofsolid, crystalline particles of desoxycholic acid as a separating agentin a countercurrent adsorption type of separation procedure. A glasstube inches long by 7 mm. ID. was packed to a length of 8% inches with3.5 grams of crystalline, desoxycholic acid. A hydrocarbon mixtureconsisting of 50 parts by weight each of iso-octane and n-heptane wascharged into the top of the column dropwise, followed by collectingfractions, each representing 10% by volume of the hydrocarbon mixturecharged, from the bottom of the column. The test was run atapproximately room temperature; that is, about 24 C. and the effluentfractions collected from the bottom were analyzed by infra-redspectroscopy to determine the ratio of iso-octane to n-heptane and thusindicate the eifectiveness of the desoxycholic acid for separating thehydrocarbon mixture. The first 10% by weight of the charge stockcollected in the efiiuent receiver contained 60 parts by weight ofiso-octane and 40 parts by weight of n-heptane, compared to the 50-50weight percent mixture charged into the top of the column. The nextefliuent fraction, comprising from 10 to 20% by weight of thehydrocarbon feed stock contained 55 weight percent iso-octane and 45weight percent aheptane.

In a second run utilizing the same feed stock mixture, a similarlypacked adsorption column and utilizing the same temperature andcollecting procedure, except that cholic acid was substituted for thedesoxycholic acid as the packing material in the adsorption column, nodiscernible enrichment of iso-octane in the efiluent fraction wasobserved, the first 10 ccs. of eflluent containing 50 weight percenteach of iso-octane and n-heptane (corresponding to the composition ofthe charging stock). The next 10% by weight of the charge was also ofthe same composition as the feed stock. Thus, cholic acid is inefiective for separating relatively straight chain hydrocarbons fromtheir branched chain homologs.

EXAMPLE IV In the following run, various hydrocarbon mixtures, ,preparedfrom C.P. grade materials to form mixtures containing knownconcentrations of the individual compovnents were utilized in achromotographic type adsorption procedure to determine the applicabilityof the method to various hydrocarbon mixtures. The adsorption columnconsisted of a glass tube 10 inches long by 7 mm. ID. and thehydrocarbon mixtures were made up by mixing equal weight proportions ofa branched chain aliphatic or cyclic hydrocarbon with a relativelystraight chain aliphatic hydrocarbon, the mixtures utilized beingtabulated in the following Table I which also indicates the degree ofseparation obtained, as measured by infra-red spectro- -scopic analysesof the efiluent fractions:

Table I OHROMOTOGRAPHIC ABSORPTION OF HYDROCARBONS FROM 5050 WEIGHTPERCENT MIXTURES First Fraction Second Frac- (First 10% by tion (SecondMixed Hydrocarbon Charge wt. of hydro- 10% by wt. of

carbons hydrocarbon charged) charged) n-pentane 38. 4 46. 5 isopentane.61. 8 62. 4 n-hexane 41. 3 45. 1 2-methylpentan 56. 1 53. 2 n-hexaue 38.2 41. 2 2,2dimethylbutane. 60. 8 59. 3 n-hexane 35. 1 3B. 9 cyclohexane63. 5 58. 1 n-dodecane 32. 1 39. 2 hydrogenated propylene tetramercomprising various highly branched dodecane isomers 65. 4 56. 3

The results indicated above establish the eifectiveness of desocycholicacid for separating hydrocarbon mixtures comprising components ofvarious degrees of branched chain structure, the greatest resolutionbeing obtained between straight chain or normal aliphatic hydrocarbonsand their highly branched chain or cyclic isomers.

I claim as my invention:

1. A process for separating a straight chain aliphatic hydrocarbon offrom 4 to about 20 carbon atoms per molecule from a mixture thereof withat least one other hydrocarbon component selected from the groupconsisting of branched chain aliphatic hydrocarbons and cyclichydrocarbons, which comprises contacting said mixture with desoxycholicacid maintained in solid phase at a temperature of from about 0 to aboutC. to selectively retain the straight chain hydrocarbon in said acidwhile rejecting said other hydrocarbon component in a rafiinate phase,and separating the rafiinate phase from the combination of thedesoxycholic acid with the straight chain hydrocarbon.

2. A process for separating a straight chain aliphatic hydrocarbon offrom 4 to about 20 carbon atoms per molecule from a mixture thereof withat least one other hydrocarbon component selected from the groupconsisting of branched chain aliphatic hydrocarbons and cyclichydrocarbons, which comprises commingling said mixture in liquid phasewith solid desoxycholic acid at a temperature of from about 0 to about120 C. to selectively retain the straight chain hydrocarbon in said acidwhile rejecting said other hydrocarbon component in a liquid phase, andthereafter filtering the admixed hydrocarbons and desoxycholic acid toseparate a filtrate enriched in said other hydrocarbon component from afilter cake comprising a combination of the desoxycholic acid with thestraight chain hydrocarbon.

3. The process of claim 1 further characterized in that said straightchain aliphatic hydrocarbon is recovered from its combination with thedesoxycholic acid by contacting said combinatiomwith a des'orbingagentcomprising -a straight chain hydrocarbon having-a boiling point whichdiffers from the boiling point of the straight chain aliphatichydrocarbon of said mixture.

'4. The process of claim 3 further characterized in that said'desorbingagent comprises n-pentane.

5. The process of claim 3 further characterized in that said desorbingagent comprises n-hexane.

6. The'process of claim 1 further characterized in that said hydrocarbonmixture comprises isomeric hydrocarbons.

7. The process of claim 1 further characterizedin that 9. The process ofclaim 2 further characterized in that said filter cake is thereaftermixed with a straight chain hydrocarbon desorbing agent havingaboilingpoint. which differsfrom-the boiling point of the hydrocarbonmixture in an amount .sufiicient to substantially completely displacethe adsorbed hydrocarbon from 'said desoxycholic acid combination.

10. The. process of claim';9. further characterized in that the mixtureformed by mixing said combination ,with said desorbing agent isfiltered, the filtrate thereafter distilled and the straight chainaliphaticrhydrocarbon component of the feed stock mixture recovered as afraction of the distillation.

References Cited in the file of this patent Rheinboldt et al.: Jour. FurPrakt. Chem, vol. 153, 2 (1939), pages 313-26, pages 313-316 only neededHuntre'ss et al.: I our. Amer. Chem. Soc., vol. 71 (1949), pages 458 60.

1. A PROCESS FOR SEPARATING A ATRAIGHT CHAIN ALIPHATIC HYDROCARBON OFFROM 4 TO ABOUT 20 CARBON ATOMS PER MOLECULE FROM A MIXTURE THEREOF WITHAT LEAST ONE OTHER HYDROCARBON COMPONENT SELECTED FROM THE GROUPCONSISTING OF BRANCHED CHAIN ALIPHATIC HYDROCARBONS AND CYCLICHYDROCARBONS, WHICH COMPRISES CONTACTING SAID MIXTURE WITH DESOXYCHOLICACID MAINTAINED IN SOLID PHASES AT A TEMPERATURE OF FROM ABOUT 0* TOABOUT 120*C. TO SELECTIVELY RETAIN THE STRAIGHT CHAIN HYDROCARBON INSAID ACID WHILE REJECTING SAID OTHER HYDROCARBON COMPONENT IN ARAFFINATE PHASE, AND SEPARATING THE RAFFINATE PHASE FROM STHECOMBINATION OF THE DESOXYCHOLIC ACID WITH THE STRAIGHT CHAINHYDROCARBON.